Practice Exam Questions And Correct

Ohio Water Treatment Operator Class B Practice Exam Questions And Correct Answers (Verified Answers) Plus Rationales 2025|2026 Q&A | Instant Download Pdf

1. The primary purpose of coagulation in water treatment is to:

• Remove dissolved gases
• Neutralize pathogens
• Destabilize colloidal particles
• Reduce hardness

 Coagulation neutralizes the charge on colloids, allowing them to clump and settle in flocculation.*

2. Alum (aluminum sulfate) is commonly used as a:

• Disinfectant 1 / 4

• pH adjuster
• Coagulant
• Corrosion inhibitor

 Alum is a coagulant used to remove turbidity and color by forming floc.*

3. Chlorine demand is defined as:

• Total chlorine added
• Residual chlorine in water
• Chlorine applied minus residual chlorine
• Chlorine used in disinfection

 Demand represents the chlorine consumed by organic and inorganic substances before residual remains.*

4. The optimal pH range for alum coagulation is generally:

A. 4.0–5.0

B. 5.5–7.5

C. 7.5–9.5

D. 9.5–10.5

 Alum works best under slightly acidic to neutral conditions for efficient floc formation.*

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5. A common indicator for chlorine residual testing is:

• Phenolphthalein
• DPD (N,N-diethyl-p-phenylenediamine)
• Methyl orange
• Bromocresol green

 DPD reagent produces a pink color proportional to chlorine residual concentration.*

6. Turbidity in treated water should not exceed:

A. 5 NTU

• 1 NTU (for most systems)

C. 10 NTU

D. 0.5 NTU

 Ohio and EPA standards generally require turbidity ≤1 NTU for conventional treatment systems.*

• Which type of valve is best used for throttling flow?
• Gate valve
• Globe valve
• Check valve
• Plug valve 3 / 4

 Globe valves allow precise flow regulation, while gate valves are for full open/close.*

8. Head loss in a filter primarily increases because of:

• Chemical addition
• Accumulation of solids
• Air binding
• Flow velocity reduction

 Solids trapped in the media restrict flow, increasing head loss.*

9. Backwashing a rapid sand filter removes:

• Dissolved minerals
• Accumulated suspended solids
• Organic matter only
• Hardness ions

 Backwashing loosens and flushes trapped solids from the filter media.*

10. The pH of water is a measure of:

• Alkalinity
• Hardness
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